This invention relates to hydraulic clutch actuators and more particularly to hydraulic clutch actuators employing a damper mechanism.
Hydraulic actuators are known for operating a mechanism at a remote location by way of a master cylinder connected to a slave cylinder installed at the remote location. A conduit interconnects the master cylinder to the slave cylinder and the hydraulic apparatus is filled with hydraulic fluid such that, when the piston of the master cylinder is actuated, the piston of the slave cylinder and consequently the piston rod or output member is simultaneously actuated by displacement of the hydraulic fluid from the master cylinder to the slave cylinder through the conduit.
More particularly, it is known to provide such a hydraulic actuator for operating the clutch of a motor vehicle so that, when the clutch pedal of the vehicle is depressed by the driver, the slave cylinder is actuated to operate the clutch in known manner. Preferably, as described in U.S. Pat. No. 4,599,860 assigned to the assignee of the present application, the clutch actuator is provided to the motor vehicle manufacturer in an assembled pre-filled form to simplify installation of the actuator on the vehicle, avoid the inconvenience of potential spillage of hydraulic fluid during on-line filling, eliminate the necessity to bleed or purge the lines of the actuator to facilitate the filling process, and eliminate the need to test the actuator after installation and filling. Whereas hydraulic clutch actuators, and particularly pre-filled clutch actuators, have enjoyed significant commercial success, they have the ability to transmit vibrations backwardly through the system from the clutch to the clutch pedal with the result that the operator may experience unpleasant vibrations at the clutch pedal.
Specifically, imbalances in the crank shaft of the vehicle engine or engine firing impulses are transmitted to the flywheel which undergoes a swashing movement, the flywheel swashing movement in turn leads to vibrations of the spring fingers of the clutch release mechanism, the vibrations of the spring fingers are transferred to the release bearing of the clutch, and the vibrations propagate backwardly through the hydraulic fluid in the slave cylinder, through the hydraulic fluid in the conduit interconnecting the slave cylinder and the master cylinder, through the hydraulic fluid in the master cylinder, and then through the master cylinder pushrod to the clutch pedal where they are experienced by the operator as vibrations of the clutch pedal. The propagated vibrations also generate a pedal growl which is audible to the operator as well as a clutch roar which may also be audible to the operator.
Various devices have been proposed in an attempt to attenuate these vibrations. For example, tuned masses have been attached to various parts of the clutch system including the clutch release lever, the slave cylinder pushrod, and the clutch pedal; rubber dampers have been employed in the master cylinder pushrod; rubber hose sections have been employed in the conduit interconnecting the master cylinder and the slave cylinder; and various damper devices have been proposed for installation in the interconnecting conduit. For example, a damper device as shown in British Patent Specification 1,562,709 or as shown in U.S. Pat. Nos. 4,998,609 or 5,320,203, all assigned to the assignee of the present invention, may be installed in the conduit interconnecting the master cylinder and the slave cylinder. More recently, and as shown in co-pending U.S. patent application Ser. No. 09/620,436 assigned to the assignee of the present invention, an elastomeric diaphragm has been proposed for use with a further spring steel diaphragm to provide a dual action diaphragm wherein the elastomeric diaphragm damps low frequency vibrations in the system and the elastomeric diaphragm deforms against the spring steel diaphragm to damp high frequency vibrations in the system. Whereas this dual action damper has been successful in damping both low frequency and high frequency vibrations in the system, the use of a stretchable elastomeric diaphragm has complicated the evacuating and filling operations necessary to prepare the damper for use in the hydraulic system and specifically has resulted in situations where the elastomeric diaphragm is stretched beyond its elastic limit during the evacuation operation and/or the damper is not fully evacuated and consequently is subsequently not fully filled.
This invention is directed to the provision of an improved damper device for use in association with a hydraulic clutch actuator.
More particularly, this invention is directed to the provision of an improved damper device which eliminates the evacuating and filling problems previously encountered with the use of a stretchable elastomeric diaphragm.
This invention relates to a damper for provision in a hydraulic actuator system between the master cylinder and a slave cylinder of the system. The damper includes a housing including a damper port for connection in the system and a diaphragm carried by the housing and coacting with the housing to define a chamber above the diaphragm and in communication with the damper port so that the diaphragm may deflect in response to vibrations transmitted through the hydraulic fluid in the system to effect damping of the vibrations.
According to the invention, the diaphragm is formed of an elastomeric material; the damper further includes a stop structure positioned in the chamber in confronting relation to the diaphragm and operative to limit upward excursions of the diaphragm into the chamber to excursions within the elastic limit of the diaphragm, and the stop structure includes aperture means providing communication between the port and the chamber irrespective of the position of the diaphragm relative to the stop structure. This arrangement precludes permanent stretching of the diaphragm during the evacuation and filling operations and allows total evacuation of the chamber and subsequent total filling of the chamber.
According to a further feature of the invention, the stop structure comprises a tube communicating at an upper end thereof with the damper port, extending downwardly into the chamber, and including a free lower end positioned proximate the diaphragm, and the aperture means includes apertures in the tube communicating the interior of the tube with the chamber. This arrangement maintains communication between the port and the chamber even with the elastomeric diaphragm pulled upwardly into a position closing the free end of the tube.
According to a further feature of the invention, the damper further includes a plurality of circumferentially spaced ribs extending radially outwardly from the tube and each defining a lower edge substantially level with the free lower end of the tube. This arrangement serves to further limit upward excursions of the diaphragm and further preclude permanent stretching of the diaphragm during the evacuation operation.
According to a further feature of the invention, the damper comprises a dual action damper wherein the elastomeric diaphragm deflects in response to the low frequency vibrations transmitted through the hydraulic fluid in the system to effect damping of low frequency vibrations, and the damper includes a further relatively stiff diaphragm carried by the housing and positioned proximate a lower face of the elastomeric diaphragm so as to form a back up to the elastomeric diaphragm. With this arrangement the elastomeric diaphragm may deform against the further diaphragm in response to high frequency vibrations transmitted through the hydraulic fluid to cause deflection of the further diaphragm to effect damping of the high frequency vibrations.
According to a further feature of the invention, the aperture means includes a plurality of circumferentially spaced apertures in the tube proximate the lower end of the tube with each aperture comprising a downwardly opening slot formed in the lower end of the tube between adjacent ribs. This specific construction provides a positive limit of upward excursion with respect to the entirety of the elastomeric diaphragm and allows total evacuation of the chamber above the diaphragm preparatory to the filling operation.
Other objects, advantages and applications of the present invention will become apparent to those skilled in the art when the following description of the best modes contemplated for practicing the invention are read in conjunction with the accompanying drawings.